1. Field of the Invention
The present invention relates to an apparatus for automatically measuring dust concentration in flue gas discharged from a heating furnace, boiler, dust collector, or the like.
2. Description of the Related Art
The Air Pollution Control Act requires that dust generating facilities such as heating furnaces and boilers have a periodic measurement of dust concentration in flue gas. The dust concentration in flue gas discharged from the dust collectors is also regulated by regional pollution prevention agreements or the like, and the measurement of the dust concentration is also required by such agreements.
An example of conventional apparatus for automatically measuring dust concentration in flue gas is given in FIG. 13 which is employed in JIS Z-8808. The apparatus comprises means for collecting dust (I), means for sucking gas (II), and means for measuring a sucked gas flow rate (III).
The dust collecting means (I) comprises a dust collector 41 which contains a filter paper 6, a Venturi tube 42, a temperature detector 43 for measuring the temperature of flue gas, and a pitot tube 9 for determining the flow rate of the flue gas. Those devices are protected by a protective tube 44, and the protective tube 44 is inserted into a measuring hole 2 on a factory gas duct 1.
The gas suction means (II) comprises a conduit 45 for sucking the collected gas, a conduit 46 for pressure transmission, a pressure gauge 47, a suction pump 14, a surge motor 48, a sucked gas flow rate regulator valve 49, a flow rate controller 50, an SO.sub.2 absorption bottle 12, and a mist removal bottle 13.
The gas flow rate measuring means (III) comprises a thermometer 51, a manometer 52, and a wet gas meter 15. The means further needs a drier and a desiccator for drying the filter paper and a balance for weighing the filter paper at the laboratory (IV), though these devices are not shown.
As illustrated in FIG. 13, the measurement specified in JIS Z-8808 is carried out by mounting the filter paper 6 in the dust collector 41 facing the flow direction of flue gas, by sucking the flue gas collected by the suction pump 14 at an equal flow rate to that in the pitot tube 9 of the dust collection means (I), by taking the filter paper 6 out from the dust collector 41, by transferring the filter paper 6 to the laboratory (IV), by drying the filter paper 6 in a drier followed by drying it in a desiccator, and by determining the weight of dust attached on the filter paper 6 using a balance. However, this type of measuring method is troublesome because it requires replacing the filter paper 6 and drying it, which makes the automatic measurement difficult.
There are several already developed methods of automatic measurement of dust concentration in flue gas, which include a light scattering method, a light permeation method, a .beta. ray absorption method, a capacitance method and so on.
Unexamined Japanese Patent Publication No. 57-128830 discloses an automatic dust concentration automatic measuring technology using the .beta. ray method. FIG. 14 illustrates a scheme of the prior art dust concentration measuring apparatus disclosed in the patent publication.
The dust concentration measuring apparatus has the following characteristics.
Reference number 101 denotes a gas sampling tube for collecting sample gas, 102 is a heating tube for introducing the sample gas, 103 is a dust collector for collecting dust in the sampled gas, 104 is a suction piping, 105 is a valve for adjusting the suction gas flow rate, 106 is a suction pump, 107 is a gas meter which generates pulses corresponding to the mass signals of the sucked sample gas, 108 is a coiled filter paper tape, 109 is a motor reel for coiling and uncoiling of the filter paper, 110 is a feed roller for feeding the filter paper back and forth, 111 is a pinch roller for securing a smooth transfer of the filter paper, 112 is a radio isotope generator which emits .beta. rays, 113 is an isotope detector, 114 is a mass calculator for computing the dust mass from the quantity of the .beta. rays permeating through the paper, 115 is a flow rate calculator for computing the flow rate from the received flow rate pulse signals sent from the gas meter 107, 116 is a concentration calculator for determining the dust concentration from the output of the mass calculator 114 and the output of the flow rate calculator 115, 117 is a sequence control circuit for controlling the action of the dust concentration meter. With these devices, the dust concentration meter is structured. Nevertheless, this type of apparatus is only used for measuring the quantity of a specific element. For this reason, this type of apparatus has a problem of poor accuracy in the measurement of concentration of dust containing various kinds of elements.
An example of a weighing method of the prior art automatic dust concentration measurement technology is disclosed in Unexamined Japanese Utility Model Publication No. 55-97631.
The disclosed technology is a type of automatic falling dust sampling and measuring unit, which automatically weighs the falling dust and which transmits the data after classifying the data according to the direction of gas flow and the amount of time. This apparatus comprises a collection funnel which collects the falling dust, a rotary table which supports more than one sample bottle, a driving unit which intermittently drives the rotary table to position each of the sample bottles, in turn, at the dust receiving point under the dust collection funnel, a weighing device which weighs the dust in the sample bottle, a circuit which classifies the collected data for each direction of gas flow and amount of time. This apparatus, however, does not include a means for providing correction of the data for the moisture content in the flue gas. For this reason, the accuracy of measurement with this apparatus is poor.